The present invention disclosed herein relates to optical modules, and more particularly, to optical modules for transmitting a high frequency signal.
In order to transmit and process a high frequency signal in a optical transmission or/and optical reception module(s) of more than about 10 Gbps, a ceramic submount is used inside a metal package and a Flexible Printed Circuit Board (FPCB) is used outside the metal package. In the ceramic submount and the FPCB, an electrode of a CoPlanar Waveguide (CPW) form is used. Also, in order to transmit a high frequency signal without reflection, a termination matching resistor is integrated on the ceramic submount with a thin-film type and in order to prevent distortion phenomenon of a high frequency signal due to resonances, via holes that electrically connect an upper ground electrode and a lower ground electrode are formed. A process for forming the thin-film type termination matching resistor and the via holes on the ceramic submount requires high costs so that it accounts for a significant portion of the total cost for fabricating an optical module. Moreover, the forming of the thin-film type termination matching resistor of a high quality on the ceramic submount or the forming of the elaborate via holes requires high technology.
Furthermore, a ceramic feed-through is formed in a metallic package body according to an optical module structure using the ceramic submount so that a high frequency transmission line of the ceramic submount in the metallic package body is connected to a high frequency transmission line formed on the ceramic feed-through through bonding wires, and a high frequency transmission line of the FPCB at the outside of the metallic package is connected to a high frequency transmission line formed on the ceramic feed-through through soldering. Generally, if a high frequency signal is connected by bonding wires through a plurality of steps, it is reflected because of characteristic impedance mismatch, so that high frequency signal characteristics of an optical module are seriously deteriorated.